mirror of https://github.com/TomHarte/CLK.git
35 lines
1.2 KiB
C++
35 lines
1.2 KiB
C++
//
|
|
// BitSpread.hpp
|
|
// Clock Signal
|
|
//
|
|
// Created by Thomas Harte on 12/10/2021.
|
|
// Copyright © 2021 Thomas Harte. All rights reserved.
|
|
//
|
|
|
|
#pragma once
|
|
|
|
namespace Numeric {
|
|
|
|
/// @returns The bits of @c input with a 0 bit inserted between each and
|
|
/// keeping the least-significant bit in its original position.
|
|
///
|
|
/// i.e. if @c input is abcdefgh then the result is 0a0b0c0d0e0f0g0h
|
|
constexpr uint16_t spread_bits(uint8_t input) {
|
|
uint16_t result = uint16_t(input); // 0000 0000 abcd efgh
|
|
result = (result | (result << 4)) & 0x0f0f; // 0000 abcd 0000 efgh
|
|
result = (result | (result << 2)) & 0x3333; // 00ab 00cd 00ef 00gh
|
|
return (result | (result << 1)) & 0x5555; // 0a0b 0c0d 0e0f 0g0h
|
|
}
|
|
|
|
/// Performs the opposite action to @c spread_bits; given the 16-bit input
|
|
/// @c abcd @c efgh @c ijkl @c mnop, returns the byte value @c bdfhjlnp
|
|
/// i.e. every other bit is retained, keeping the least-significant bit in place.
|
|
constexpr uint8_t unspread_bits(uint16_t input) {
|
|
input &= 0x5555; // 0a0b 0c0d 0e0f 0g0h
|
|
input = (input | (input >> 1)) & 0x3333; // 00ab 00cd 00ef 00gh
|
|
input = (input | (input >> 2)) & 0x0f0f; // 0000 abcd 0000 efgh
|
|
return uint8_t(input | (input >> 4)); // 0000 0000 abcd efgh
|
|
}
|
|
|
|
}
|